Concanavalin A (con A) is one of several lectins which have been found to stimulate mitosis, in addition to causing agglutination of cells. This protein is the most extensively studied of the group, and X-ray studies in other laboratories have already established its three dimensional structure. Its biological effects appear to arise entirely from its ability to bind saccharides. Attempts are being made, with the aid of circular dichroism and other optical methods, to obtain information on structural modifications within the con A molecule resulting from a variety of reactions, and to relate these changes with modifications in biological activity, as part of an investigation of mitogenic effects as a long range goal.